The present application relates to antenna systems and, more particularly, although not exclusively, to microwave antenna systems that have beam widths that may be varied.
Microwave antennas are used for transmission and reception of microwave electromagnetic-radiation signals. A microwave antenna will have a particular characteristic beam pattern. This beam pattern typically includes a main lobe. The dimensions of the main lobe define the beam width for the principle transmission/reception beam for the antenna. A typical beam pattern also includes a number of side lobes. These side lobes reduce the transmission efficiency (as they typically represent lost signal power), but generally do not significantly impact alignment of the microwave antenna. The beam width of the main lobe—which is typically measured in terms of the angle subtended by the main lobe—is inversely proportional to the frequency of the signals transmitted by the antenna and to the effective size of the antenna. In other words, (a) the higher the operating frequency, the narrower the beam width, and (b) the larger the antenna, the narrower the beam width.
A microwave transmission link comprises a pair of distant antennas, namely a first antenna that transmits a microwave signal and a second antenna that receives the microwave signal. A thin—in other words, narrow or pencil—beam between the two antennas is more useful than a fat—in other words, wide—beam for efficiently transmitting signals between those two antennas since much more of the signal energy is directed from the transmitter to the receiver with a thin beam than with a fat beam. When setting up the two antennas for the transmission link, however, using a thin beam is more challenging than using a fat beam for alignment of the boresights of the respective antennas since a thin beam is more difficult to acquire and pinpoint than a fat beam.